One idea that’s been on my mind: rather than search for answers deep in the heart and soul of impact investing, we should look at the history of index funds.

The foundational academic article about indexing as an investment strategy was written 50 years ago, in a piece penned in 1966 by William Sharpe in The Journal of Business. Sharpe’s conclusion, among others, was that “The results tend to support the cynics: good performance is associated with low expense ratio.” Not shocking, but this was the opposite of the core logic of the mutual fund industry, one which justified high expenses by supposedly even higher performance.

Nine years after Sharpe’s article, in 1975, John Bogle founded the Vanguard Group, and in 1976 he launched Vanguard 500 (VFINX). VFINX was and is a low-cost fund that mirrors the S&P 500. Investors in the fund are“buying” the entire S&P for a very low cost. The theory was simple: you won’t beat the S&P in the long run, so the smart thing to do is to get the S&P’s returns with as low an expense ratio as possible.

This one fund was a bet that, over time, investors would come to understand that consistently beating the market with an active stock-picking strategy is hard, and that beating the market by enough to make up for the cost of active management is nearly impossible.

(For some simple math to support this conclusion, think of it this way: historic equity returns are about 7% a year, and most mutual funds charge around 1.5% in fees (if not more). This means you’re eating up more than 20% of your return every year with the fees paid to an active manager. The assets that manager invests in needs to beat the market by more than 20% every year, forever, just to match the performance of an indexed fund. It turns out that this is very hard to do. A 1991 article by Sharpe drilled the point home: “To repeat: Properly measured, the average actively managed dollar must underperform the average passively managed dollar, net of costs. Empirical analyses that appear to refute this principle are guilty of improper measurement.” Now, this would be obvious if fund fees were sold as “20% of total expected return” instead of “1.5% of invested capital.” But I digress.)

Despite the analytical support of academics like Sharpe and others, Bogle and the Vanguard Group were often mocked, and even called un-American, for their tortoise-like strategy of mirroring the broader market instead of trying to beat it, all while charging investors spectacularly low fees. This strategy cut deeply against the story, heavily marketed by the big banks, that mutual fund managers added value to their clients, value that was more than offset by the fees they charged. The mutual fund industry exists to do many things, and one of those things to preserve itself. There was a lot to be lost with the growth of indexing, not only huge profits but also the very American story that it’s better to bet on the chance of winning than it is to be certain not to lose. These two reasons – marketing power and unchecked investor naiveté – are why it took so long for the facts to prevail.

And yet, despite institutional and cultural resistance, time is a powerful tool. Indexing has grown, ever so slowly, as a proportion of the market over the last four decades, reaching 20% of U.S. equity mutual fund assets in 2014. More interesting still, in the last three years, Vanguard’s assets under management have grown faster than the rest of the mutual fund industry combined. That’s right, according to a recent New York Times article, in the last three years, the entire mutual fund industry, more than 4,000 firms, took in $97 billion, and Vanguard took in $823 billion. Vanguard now manages $4.2 trillion in mutual fund assets, having quadrupled its assets under management in the last 7 years.

If this is analogous to what it will take to “mainstream” impact investing, then we have a few lessons to take away.

First, this is a long road we are walking. So let’s be prepared for a marathon, not a sprint. This means it’s time to stop, as we enter the end of our first decade, pretending that the tipping point is just around the corner.

Second, better data and facts, even for something as easily analyzed as public mutual fund returns, are hard to come by, easy to dispute, and alone they are not enough to tip the scales.

Third, economic incentives are powerfully aligned for the gatekeepers to keep things the way they are. Despite this, things can shift massively if clients speak loudly and uniformly.

Fourth, even a robust story that shouted “this is a better way to make money!” took 50 years to penetrate the prevailing wisdom. We’re twisting ourselves into knots to publish a handful of reports saying there aren’t financial trade-offs between impact investing and other approaches. It’s great to know that is possible. But data alone doesn’t tip the scales, what’s needed is a shift in mindset and a better story. And “we can make as much money as you” strikes me, in the face of the history of indexing, as weak sauce.

Finally, a request. I wasn’t able to uncover a proper analysis of the key milestones in the growth of indexing, but I’d love to find one. For anyone interested in growing the share of investment capital that takes social returns, stakeholders, the long-term view, the environment…anything beyond traditional thinking into account, I suspect that the rocky history of indexing holds more than a few clues about the pitfalls we can avoid and, hopefully, provides a map for shortening our 50-year journey just a bit. The world needs us to move faster than that.